In each central arm there are three thin layers of pad chambers that provide
three-dimensional coordinates along the charged particle trajectories in the
field-free region. The total area of the pad chambers exceeds 100
m2, and the main function is to ensure reliable pattern recognition
in the high-multiplicity enviroment at RHIC.
The first layer called PC1 has 8 chambers in each arm of
multi-wire proportional chambers. The PC1 is placed immediately behind the
drift chamber and in front of the ring-imaging Cherenkov detector (RICH). The
PC2 and PC3 each have 4 chambers in each arm that are located after the RICH,
on both sides of the time expansion chamber (TEC).